1. Field of the Invention
The present invention relates to a method for treating oily wastes by forming the waste into granules. More particularly, the method uses a high speed mixer to form granules of a discrete size, from which a portion of the contaminating hydrocarbons may be removed.
2. Description of Related Art
Treatment of oily waste material and, especially soils and particle fines which have been burdened with oily materials, has been and continues to be a problem. In the past, various methods have been used in an attempt to consolidate or to encapsulate the material prior to further treatment or to disposal of the material.
One method to treat oily wastes is to extract the hydrocarbons from the oily waste with a solvent. An example of a method is disclosed in U.S. Pat. No. 4,931,161, the disclosure of which is incorporated herein by reference, involves adding solids to the oily waste, then granulating the mixture. The granules are then contacted with a solvent to recover the hydrocarbons. The process however, produces granules of varied size and must be crushed and screened for uniformity.
Another method of treating the oily waste is to mix the waste with water containing modifiers under conditions that result in the material forming a slurry. The modifiers enhance the scrubbing effect of the water. However, a major consideration of all washing techniques is the fact that as the particle reject size decreases, handling and cleaning efficiency likewise decreases. This requires the fines to be separated by centrifuges, belt filters, and other costly methods known in the art. Because these fine particles are carried out of the cleaning system relatively early they contain higher amounts of harmful substances and may also constitute more than 30% of the soil being treated.
Another method is to convert the oily waste material to a substantially impermeable, load-bearing construction material. U.S. Pat. No. 4,514,307 provides an example of such a method. According to the '307 patent, waste material is combined with cementitious reactants consisting essentially of lime and fly ash, in the presence of water, to form a mixture in which the relative proportions of the waste material, linde, fly ash, and water are adapted to permit the lime and fly ash to react at atmospheric conditions and thus to form a cementitious matrix in which the waste material is encapsulated.
Still another method of treating oily wastes involves combining the waste with solids and then incinerating the mixture. U.S. Pat. No. 4,775,457 provides an example of such a method. According to the '457 patent crude oil and other heavy hydrocarbon sludges are mixed with adsorbent material, preferably an earth material, such as diatomaceous earth or perlite, and oxidized in an incinerator or calciner to produce gaseous combustion products and a friable solids material which is substantially hydrocarbon free and may be recycled for mixture with the incoming sludge stream or otherwise disposed of in an environmentally acceptable manner.
A disadvantage in using any of the aforementioned processes is that the particle size, to a large degree, is random. Particles may range in size from less than 0.003 to greater than 3 inches. This non-uniformity significantly hinders hydrocarbon removal from the granules in subsequent process steps.
It is, therefore, a principal object of the present invention to provide a method for producing free flowing granules having a discrete size. Preferably, the granules have a particle size of less than about 0.5 millimeters. As used herein, the term "free flowing" is defined as a powder that flows freely with no bridging in the bulk when withdrawn from the bottom of a conical hopper having a 30.degree. included angle.
It is another object of the invention to improve the efficacy of solvent extracting the hydrocarbons from the granules. These and other objects are accomplished by the invention set forth in the description and examples below.